基于工业CT图像重构的网格模型的保特征简化方法

对基于工业CT图像重构的网格模型进行网格简化时,大多数现有网格模型简化算法会丢失特征,出现网格质量不好的问题。因此提出一种网格模型保特征简化方法,该方法用三角形折叠法对原始模型进行简化,当简化后模型的平均二面角角度误差达到允许误差后,再使用边折叠法对模型进行简化。在三角形折叠法中提出了利用被折叠三角形的法向量、各个顶点的高斯曲率及其在周边三角形上的投影确定该三角形的折叠点,利用局部体积误差与二面角角度误差的无因次化和确定折叠代价的方法;在边折叠法中提出了将二面角角度误差引入到二次误差测度（QEM）法的折叠代价中的改进QEM法。实验结果表明：与其他算法相比,该方法能够生成保特征、高质量、低几何误差的网格模型。     

ZrCuSiAs型锰基化合物ThMnSbN中的化学压力效应

采用固相反应法合成了一种Zr Cu Si As型准二维层状锰基化合物Th Mn Sb N.基于X射线粉末衍射的结构精修显示,该化合物属于P4/nmm空间群.其晶胞参数为a=4.1731?, c=9.5160?.电输运测量显示,该化合物电阻率随温度下降缓慢上升,且在16 K附近出现电阻率异常.与此同时,该材料的磁化率在同一温度附近出现异常,显示出类似磁性相变的行为.进一步的比热测量中没有观察到磁相变导致的比热异常.另外,低温下的比热分析显示,该材料的电子比热系数为γ=19.7 m J·mol^–1·K^–2,远高于其他同类锰基化合物.该结果与电输运测量中观察到的低电阻率行为相符,暗示Th Mn Sb N中费米面附近存在可观的电子态密度.基于对一系列Zr Cu Si As型化合物晶体结构细节的比较,分析了含有萤石型Th₂N₂层的系列化合物中导电层所受化学压力的不同作用形式.     

碳化硅中点缺陷对热传导性能影响的分子动力学研究

碳化硅(SiC)由于性能优异,已广泛应用于核技术领域.在辐照环境下,载能入射粒子可使材料中的原子偏离晶体格点位置,进而产生过饱和的空位、间隙原子、错位原子等点缺陷,这些缺陷将改变材料的热物性能,劣化材料的服役性能.因此,本文利用平衡分子动力学方法(Green-Kubo方法)采用Tersoff型势函数研究了点缺陷对立方碳化硅(β-SiC或3C-SiC)热传导性能的影响规律.研究过程中考虑的点缺陷包括:Si间隙原子(Si_Ⅰ)、Si空位(Si_Ⅴ)、Si错位原子(Si_C)、C间隙原子(C_Ⅰ)、C空位(C_Ⅴ)和C错位原子(C_Si).研究结果表明,热导率(λ)随点缺陷浓度(c)的增加而减小.在研究的点缺陷浓度范围(点缺陷与格点的比例范围为0.2%—1.6%),额外热阻率(Δ_R-R_defect-R_perfect,R=1/λ,R_defect为含缺陷材料的热阻率,R_perfec...     

硼烯/石墨烯异质结缺陷态电子结构的第一性原理研究

采用密度泛函理论系统研究了硼烯-石墨烯异质结中缺陷态对体系电子结构特性的影响.发现缺陷态存在于石墨烯一侧时会破坏异质结结构;但缺陷态存在于硼烯一侧时异质结结构仍然会稳定存在,并且体系电子结构随缺陷态密度改变而发生明显变化:从无缺陷态时的金属特性变为多缺陷态时的半导体特性.常温下的分子动力学模拟进一步验证了相关体系的动力学稳定性.     

Determination of the surface states from the ultrafast electronic states in a thermoelectric material

We reveal the electronic structure in Yb Cd₂Sb₂,a thermoelectric material,by angle-resolved photoemission spectroscopy(ARPES)and time-resolved ARPES(tr ARPES).Specifically,three bulk bands at the vicinity of the Fermi level are evidenced near the Brillouin zone center,consistent with the density functional theory(DFT)calculation.It is interesting that the spin-unpolarized bulk bands respond unexpectedly to right-and left-handed circularly polarized probe.In addition,a hole band of surface states,which is not sensitive to the polarization of the probe beam and is not expected from the DFT calculation,is identified.We find that the non-equilibrium quasiparticle recovery rate is much smaller in the surface states than that of the bulk states.Our results demonstrate that the surface states can be distinguished from the bulk ones from a view of time scale in the nonequilibrium physics.     

Cr（V）与H2络合物的EPR信号

Cr交换丝光沸石在氢气氛中强烈还原并冷却后,出现了一个各向同性的EPR信号,g值2.003,△H_PP 13.4 gauss.采用EHMO方法计算了各种可能模型化合物的g值,结果建议这一信号对应Cr(V)与H₂分子形成的络合物。     

非线性演化方程孤立波的同伦分析法求解

利用同伦分析法求解了Burgers方程，得到了其扭结形孤立波的近似解析解，该解非常接近于相应的精确解.结果表明，同伦分析法可用来求解非线性演化方程的孤立波解.同时，也对所用方法进行了一定扩展，得到了Kadomtsev-Petviashvili(KP)方程的钟形孤立子解.经过扩展后的方法能够更方便地用于求解更多非线性演化方程的高精度近似解析解. 关键词： Burgers方程 同伦分析法 KP方程 孤立波解     

The melting curve of CaSiO3 perovskite under lower mantle pressures

The high pressure melting curve of CaSiO₃ perovskite is simulated by using the constant temperature and pressure molecular dynamics method combined with effective pair potentials for the first time. The simulated results for the partial radial distribution function all compare well with experiment. The calculated equation of state is very successful in accurately reproducing the recent experimental data over a wide pressure range. The predicted high pressure melting curve is in good agreement with the experimental ones, and the melting curve up to the core–mantle boundary pressure, being very steep at lower pressures, rapidly flattens on increasing pressure. The present results also suggest the validity of the experimental data of Zerr and Boehler.     

Q-switched operation of an in-band-pumped Ho:LuAG laser with kilohertz pulse repetition frequency

We report continuous-wave (CW) and repetitively Q-switched operation of an in-band-pumped Ho:LuAG laser at room temperature. End-pumped by a Tm:YLF solid-state laser with emission wavelength of 1.91 μm, the CW Ho:LuAG laser generated 5.4-W output at 2100.7 nm with beam quality factor of M ²～1.03 for an incident pump power of 14.1 W, corresponding to slope efficiency of 67% with respect to absorbed pump power. Up to 1.5-mJ energy per pulse at pulse repetition frequency (PRF) of 3 kHz and 4.5-W average power with FWHM pulse width of 28 ns at 5 kHz were demonstrated in repetitively Q-switched operation.